your asking me how it worked under the bonnet? i don't know. All i know is that if i change a number from 0x800A0000 to 0x80400000 the regular music stops and gutair music plays, and if i use an even higher value then both Regular and Guitar melodys play. I guess it is some some sort of selector.
And yes, i used the wrong wording, and shouldn't have said "instrument bank" and said...something else.